GeologyRocks

Hello Ruby, and welcome to GR.

What are you going to do - plan a house on a lava field???  Solid foundation - for a while, but overall probably a little dodgy!

Joking aside, of course we will help if we can.  I've never been to Lanzarotti, so uploading pictures would be very helpful. 

I will make some enquires regarding geological maps, but I suspect that it will simply be defined as 'igneous rocks'.

Igneous rocks are a melt , and what the actual lava (molten rock above ground) is depends on the chemical signature of the magma   (molten rock below ground at around 1,100⁰C) which depends on the origin of the feeds to the magma chamber and what country rocks have melted into the magma (stopping), whether there has been any differentiation (as the magma chamber expels the magma it can change in constituency)

So lots to consider.  Every volcano is different.

Igneous rocks are generally heavier than sedimentary and most metamorphic rocks, except some lavas which are incredibly light because of bubbles, and I understand, an extremely good insulator.  I think the Icelanders cut it out and use it as building blocks.

There are a number of minerals that might well appear in a lava, but agin dependant on the chemical signature.  The main one that springs to mind is olivine (or olivinite) and the gem form of this is peridot, which you may well have seen in jewellery.

 I shall see what I can come up with.  I know a guy who used to go there regularly.  I'll try to contact him

  John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

Hello John,

thankyou very much for your reply, I will try to attatch some images. We were told there was a high Iron content in the area, and I think we did see olivine (is this a pale green crystal).  There are some amazing formations where the lava has cooled rapidly leaving amazing patterns.

There are also different qualities to the looser stones, some are very crumbly and matt whereas others are hard and reflective, like oil. I have photos of this somewhere as well.

I tried to paste the photos into the comments box but that doesn't seem to work, will upload to my blog instead and send you the adress

I look forward to hearing from you, thank you for your help

Ruby 

Here is my blog, the most recent post contains some of the images, I have literally thousands though so if you need me to upload more just ask!

http://plasterandpaper.tumblr.com/

Thanks again for your help, its much appreciated

Ruby

Hi,

Had a look through the blog (toad in the hole looks really good!), but I simply don't have the time to run the clips, and I'm not sure I'd understand them if I did.

But the pictures of lava are helpful.  Yes, it is iron rich hence the red oxidation known as red bole, and quite common in lavas.  Generally due to weathering.

You mention that some was rubbley and some formed patterns.  Quite right.  Lava comes in two forms, and both have Polynesian names.  This is not a wind up!

Aa Aa which is the rubbley, blockey lava. Very sharp.

Pahoehoe (pa-ho-e-ho-e) which means rope-like and this is one that 'flows' into patterns.

So it all depends on the viscosity of the lava, which come back to chemical signature in most cases, but also to the temperature.

Now the way I teach my students to remember is that the Polynesians walk around bare foot.  When they try to cross the rubbley broken lava they go 'Aa Aa!'   Yeah, I know dead corny - but I bet you never forget that!

In fact I've got asweat shirt embroidered with "Aa aa - probably the worst lava in the world" 

Volcanoes are refered to as 'red' or 'grey'. The red refers to molten red lava, which in the main is pahoehoe.   An example of this is found in the Hawian eruption and some of the Icelandic ones.  The grey, surprisingly the more dangerous of the two, is more to do with ash, pumice etc.  Theseare the ones which can produce the dreadful pyroclasstic flow (wiped out Pompii and St. Pierre  on Martinique, and killed a number of people in the Phillipines, including the Krafts .)   It is also sometimes known  by the French name - Nuee Ardente (my spelling is probably very bad but that is it phonetically) which means glowing cloud. These things can reach speeds of 200 mph - so no chance of out running them.  These are far more common Mt St Helens, Monserat, Merapi etc. 

Yes olivine is green. It can range from pale to dark, but is generally an olive green - surprise surprise!  In the Auvergne in France it is available by the bucket full.

Obviously this is all only in the broadest terms, and I'm not sure what else would be relevant to what you need for your course.  I suggest you simply ask direct questions.  Theres lots of people on here who will help where they can.

  John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

Hello,

The project is going well so far, I've managed to identify most of the rock types on the site, which is characterised by a high basalt content.

I was wondering if you could suggest any good sources to find out what the deeper  layers of sediment could be, under the surface. Some kind of geological section, are there any good websites or books that might have this information? Or am I being a bit optimistic?

My project is based on the concept of layers of time, and so obviously the layers of rock will play an important role, but I cannot find any information so far on what the island is made up of under the top few metres of soil.

 Anything at all would be helpful!

Ruby

Oh dear Ruby,

You seem to have chosen an area which most student have trouble really getting their head round - geological time.   I'm not sure any of us can really appreciate the full implications and size of it, we simply come to accept it and get used to it.

There are many sites that will give you a diagram and write up of geological time.

As you will be aware it is broken up into Periods - Pre Cambrian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous and Eocene.      

Perhaps easier to remember with the mnumonic :- Pre Cam Camels Often Sip Devon Cream Perhaps Trying to Justify Creation --- then Eocene......its so silly you will never forget it.

If we now think of the whole of geological time compressed into a year the Pre Cambrian lasted from the stoke of midnight on 1st Jan until somewhere into mid October!  The dinosaurs died out 30 minutes before the end of the year and Man appeared around 15 seconds to midnight on 31st December.  It sort of puts us in our place doesn't it?

All rocks are made up of minerals, and minerals are really a bunch of chemicals which have formed together in the right amounts in the right conditions.  They have then been subjected to further heat, pressure or erosion (google The Rock Cycle) to break down and form other rocks.  Its a slow process in most cases, but its had plenty of time to achieve its aims.  And its still going on and will always go on long so long as there is tectonic movement and atmosphere and certain after we have disappeared.

lava, basalts and other igneous rocks appear very quickly, but have been millions of years in the making.

Does that help at all, or am I on the wrong track?

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

Geological time is to geologists what the economy is to the chancellor of the exchequer - it's got too many numbers in it to make any sense.  We go on airily about the closure of the Iapetus Ocean as if it it happened in our back gardens yesterday but none of us has any idea what really happened (at least I haven't).  Having said that it's always a good idea to start a field trip with the phrase "In order to understand what's going on here we have to go back 275 million years to a time when..." etc, etc. However, first you've got to establish that nobody else knows more about the subject than you, then you're free to go waffling on to your heart's content without anyone being the wiser.

Talking of waffling on, I think I've forgotten what this post was originally about.

Dear Ruby,

 I read your messages and the replies from others. While I am not a volcanologist, my holidays all over Lanzarote allowed me to appreciate the geological and geographical variety across the island. 

Several UK university geology departments take field courses to Lanzarote, and there is a field guide published by the Geologists' Association in 2000. Also there is a good range of earth-science papers in peer-review journals on the geology, geography and biology of Lanzarote. If you google "Lanzarote history geology" you will get pages and pages of hits, some of which contain overviews of the geology.

 However, none of this is likely to help you as an architecture student; one issue in your original query is that you did not state what you were doing on Lanzarote; i.e. what is the aim of your project? If you can tell me that, then maybe I can say more. However, if for example you are considering the site of a new building, and wish to address architectural aspects, then the kinds of things you would want to know are: ground stability, rainfall (flash floods occur in Lanzarote), soil types, road access, services provision (water, electric). One really important point to note, regardless of how much you learn about the geology of Lanzarote, is that it has a complex and varied geological history. This means that from place to place across the island, the ground conditions in any one place are likely to be unique, so the more information you have about precision in location, the better your analysis can be. There are two fundamental types of volcanics that are likely to be of importance in any architectural approach:

1) lavas, of basalt, which form firm substrates for construction;

2) ashes, also of basalt, which are much less consolidated, and also tend to weather into easily erodable substrates.

Ashes form the volcanic cones, but there are some lava flows down the cone sides. But on flat or gently sloping land, you could get either in any one place or perhaps a sequence including both. I have seen numerous ash cones which have both layers of ash and solid lavas interlayered together from successive eruptions.

Regarding sediments underground, basically there aren't any, Lanzarote is made of layers of volcanic rock. However, some older lavas and ashes have been weathered in ancient times forming soils and crumbly rock, and then new lavas and ashes deposited on top, easily visible in road cuts. Weathered layers undergound may need piles to provide sufficient ground stability for a large building.

Regarding iron in the rocks; since the rocks are basalt, they are naturally rich in iron, which is why you see brown soils everywhere, from the oxidation of iron. Thus this is of no great importance since iron is everywhere.

Regarding olivine, this is arguably the most exciting geological material; it comes from the upper layers of the Earth's mantle, and is carried up in fragments inside volcanic necks to be erupted with the lavas; thus it is from a minimum of 10km down beneath the ground. The upper mantle of Earth is made essentially of olivine (iron-magnesium-silicate). If you bought/found any samples (they occur all over the island), you can WOW your friends with that snippet of info.

By the way, with all due respect to Gus, one of the commenters in the list, the concept of geological time is perfectly understandable to geologists, and the existence of many names and numbers allows geologists to refine their research to greater degrees. So this is not something to be frightened of, or confused by, but is a tool to use to understand Earth history. For your project, depending on exactly where you are focused on, the rocks are likely to have a relatively simple history; again, if you can be more precise about exactly where you are working and what the aims of the project are, then it should be possible to be more clear about the rocks in that area and how variable they are likely to be. I suspect that over a short distance of ground, the geological conditions will not vary very much in your study area around Tias, since that part of the island consists essentially of one phase of volcanics, but if you know the precise locations, then comparison  with published geological maps will soon reveal how much complexity your area has.

I hope these points are useful. Do respond if you have more questions, but I recommend you spend some time searching the pages of google hits for information first and try to solve the problems for yourself.

Best wishes

 Stromatocaster